1. Field of the Invention
The present invention relates to a method and a device for generating a sheet metal model that can be unfolded automatically, from a solid model obtained by modeling a schematic solid shape of a sheet metal product, by a simple operation in a three-dimensional sheet metal CAD/CAM system.
2. Description of the Prior Art
In the conventional three-dimensional sheet metal CAD/CAM system, a sheet metal model is usually generated by one of the two methods explained as below. A first method is shown in FIG. 1. In this method, a so-called paper model having zero thickness as shown in (a) is generated first. Then, a sheet metal model as shown in (b) is generated by offsetting the paper model in the thickness direction. This type of method for generating a sheet metal model is explained in Japanese unexamined patent publication No. 11-175575, for example.
A second conventional method for generating a sheet metal model is shown in FIG. 2. In this method, a base portion (plane) of a sheet metal product is generated by using a plate model having a thickness as shown in (a) first. Then, a bending portion is added to an edge portion of the base portion so that the sheet metal model as shown in (b) is generated.
In the above-mentioned first conventional method for generating a sheet metal model, there is a case where it is difficult to represent a shape of a sheet metal product having a thickness. For example, when generating side faces 101′ and 102′ of the sheet metal model by offsetting two neighboring side faces 101 and 102 inward by a distance of thickness as shown in FIG. 3, an interference will be generated between the neighboring side faces 101′ and 102′. In order to avoid this interference, it is necessary to keep a gap previously as shown in a portion 103 enclosed by a broken line. Such an operation is burdensome with some difficulty when the shape becomes complicated.
In addition, the above-mentioned second conventional method for generating a sheet metal model has a disadvantage that it takes a long time for modeling a product. Moreover, if side faces 105, 106 and 107 that are bending portions from the base plane 104 are not perpendicular to the base plane 104 (i.e., if they are inclined planes) as shown in FIG. 4, it becomes difficult to represent a shape of a sheet metal product. Namely, it becomes difficult to make a form of a joining portion between the neighboring side faces (e.g., side faces 105 and 106).
It is not desirable to force a designer to use a special modeling method only for designing a sheet metal product under an environment where a three-dimensional CAD is commonly used for designing. If a three-dimensional CAD system that is mainly used for designing a solid model can be used for designing a sheet metal model that can be unfolded automatically, in the same manner as a usual machine component, the system will be accepted by designers easily.